The present invention relates to a rubber composition providing rubber products which are excellent in aging resistance, and a pneumatic tire.
In order to prevent aging of rubber products using rubber compositions comprising natural rubber and/or synthetic rubber, various antioxidants have so far been developed.
Further, in order to meet social demands for saving resources and energy in recent years, low heat generation property rubber compositions have actively been developed in the rubber industry.
In general, diphenyldiamine based and hindered phenol based compounds have so far been used as antioxidants. These compounds give H of  greater than NH and xe2x80x94OH to peroxy radicals produced in a process of auto-oxidative degradation to deactivate them, and the compounds themselves turn to stable compounds through more stable radicals. Widely known is such a method that peroxy radicals are deactivated to cut off a radical chain reaction, whereby aging is prevented.
However, both the conventional diphenyldiamine based and hindered phenol based antioxidants described above have an aging-resistant action. In general, the aging-resistant effect increases according as the compounding amount is increased in a range where the compounding amount thereof is small. However, when they are used in large quantities, an increase in the effect gets slow gradually, and the effect is reduced by blooming in a certain case. Accordingly, amount to be used has to be properly restricted.
Further, the diphenyldiamine based antioxidants cause a large change rate of an elastic modulus of rubber before and after degradation of the rubber, and in a certain case, they harden the rubber markedly and deteriorate the rubber properties depending on the ingredients of the rubber composition and the conditions of degradation.
On the other hand, with respect to the aging-resistant characteristics of hydrazide compounds, known are dihydrazide compounds displaying a green strength-improving effect (U.S. Pat. No. 4,124,750), compounds which elevate ozone resistance and in which hydrogen parts of hydrazide and hydrazine are substituted (British Pat. No. 909753) and compounds having an effect as stabilizers for oil extended rubber (British patent 1330393).
Further, it is described in Japanese Pat. No. Publication No. Hei 7-57828 that specific hydrazide compounds can provide a rubber product with a low heat generation property effect and among these compounds, particularly isophthalic dihydrazide (IDH) and 3-hydroxy-2-naphthoic hydrazide can reveal a low heat generation property effect in small amounts.
However, the hydrazide compounds described in these publications, which are compounded into rubber compositions comprising a general sulfur-vulcanizing base rubber, shorten initiation of vulcanization reaction to a large extent and elevate the Mooney viscosity, so that the workability is damaged to a large extent. Accordingly, the compounding amount is restricted only to a small amount, and the satisfactory aging resistant effect is not obtained.
In light of the conventional problems described above, the present invention intends to solve them, and an object thereof is to provide a rubber composition providing rubber products having an excellent aging resistant characteristic and a rubber composition in which workability is not reduced when blended with sulfur vulcanizing agents used extensively in the rubber industry including tire.
Another object of the present invention is to provide a low heat generation property rubber composition which can control an increase in the Mooney viscosity and enhance the workability while maintaining the low heat generation property.
In addition, a further object of the present invention is to provide a pneumatic tire having an excellent aging-resistant characteristic as well as an excellent low heat generation property.
Intensive investigations of the conventional problems described above continued by the present inventors have resulted in newly finding that specific hydrazide compounds obtained as a result of modifying a hydrazide group by various methods so that an influence is not exerted on a vulcanization reaction can achieve the objects described above while maintaining an aging-resistant capability and that some of these compounds have a low heat generation property effect as well, and thus the present invention has come to complete.
That is, the present invention has the following constituents of (1) to (17):
(1) A rubber composition prepared by compounding 0.05 to 20 parts by weight of at least one selected from the group consisting of hydrazide compounds represented by the following Formulas (I) to (IV) per 100 parts by weight of a rubber component comprising at least one rubber selected from the group consisting of natural rubber and synthetic rubber: 
wherein A represents one selected from the group consisting of an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, a hydantoin ring which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, and a saturated or unsaturated linear hydrocarbon having 1 to 18 carbon atoms; R1 to R4 each represent hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group or an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, and each of R1 to R4 may be the same or different, and when R1 and R2 and/or R3 and R4 are alkyl groups, R1 may be bonded to R2 and R3 may be bonded to R4 to form rings; 
wherein Y represents hydrogen, an amino group, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group, an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, a pyridyl group or hydrazino group, R5 and R6 each represent hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group or an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, and each of R5 and R6 may be the same or different, and when R5 and R6 are alkyl groups, R5 may be bonded to R6 to form a ring; 
wherein R7 and R8 each represent an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, an alkenyl group, an amino group or an alkylamino group and each of R7 and R8 may be the same or different; and X represents a single bond or any of the groups represented by the following formulas; 
wherein R9 represents hydrogen, an alkoxy group, an amino group, a substituted amino group, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group or an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms; and R10 and R11 each represent hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group, an alkenyl group or an aromatic group which may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms, and each of R10 and R11 may be the same or different, and when R10 and R11 are alkyl groups, R10 may be bonded to R11 to form a ring.
(2) The rubber composition as described in the above item (1), containing 30 phr or more of natural rubber (which may be polyisoprene rubber) as the rubber component.
(3) The rubber composition as described in the above item (1) or (2), prepared by further compounding 20 to 150 parts by weight of a reinforcing filler.
(4) The rubber composition as described in the above item (3), wherein the reinforcing filler is carbon black.
(5) The rubber composition as described in any of the above items (1) to (4), wherein A in Formula (I), Y in Formula (II), R7 in Formula (III) and R9 in Formula (IV) in the hydrazide compounds represented by Formulas (I) to (IV) described above represent a phenyl group (may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms) or a naphthyl group (may be substituted with at least one substituent containing at least one atom of carbon, sulfur, oxygen and nitrogen atoms).
(6) The rubber composition as described in the above item (5), wherein the compound represented by Formula (I) described above is N2,N4-di(1-methylethylidene)isophthalodihydrazide, N2,N4-di(1-methylpropylidene)isophthalodihydrazide or N2,N4-di(1,3-dimethylbutylidene)isophthalodihydrazide.
(7) The rubber composition as described in the above item (5), wherein the hydrazide compound represented by Formula (II) described above is Nxe2x80x2-(1-methylethylidene)salicylohydrazide, Nxe2x80x2-(1-methylpropylidene)salicylohydrazide, Nxe2x80x2-(1,3-dimethylbutylidene)salicylohydrazide, Nxe2x80x2-(2-furylmethylene)salicylohydrazide, 1-hydroxy-Nxe2x80x2-(1-methylethylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(1-methylpropylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(1,3-dimethylbutylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(2-furylmethylene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1-methylethylidene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1-methylpropylidene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1,3-dimethylbutylidene)-2-naphthohydrazide or 3-hydroxy-Nxe2x80x2-(2-furylmethylene)-2-naphthohydrazide.
(8) The rubber composition as described in the above item (5), wherein the hydrazide compound represented by Formula (III) described above is N-benzoyl-Nxe2x80x2-phenylhydrazide, 1-benzamidoguanidine or 1-benzoylsemicarbazide.
(9) The rubber composition as described in the above item (5), wherein the hydrazide compound represented by Formula (IV) described above is Nxe2x80x2-(1-methylethylidene)benzenesulfonohydrazide, Nxe2x80x2-(1-methylpropylidene)benzenesulfonohydrazide, Nxe2x80x2-(1,3-dimethylbutylidene)benzenesulfonohydrazide, Nxe2x80x2-(1-phenylethylidene)benzenesulfonohydrazide, Nxe2x80x2-(2-hydroxybenzylidene)benzenesulfonohydrazide, Nxe2x80x2-diphenylmethylenebenzenesulfonohydrazide, Nxe2x80x2-(2-furylmethylene)benzenesulfonohydrazide, Nxe2x80x2-(1-methylethylidene)-p-toluenesulfonohydrazide, Nxe2x80x2-(1-methylpropylidene)-p-toluenesulfonohydrazide, Nxe2x80x2-(1,3-dimethylbutylidene)-p-toluenesulfonohydrazide, Nxe2x80x2-benzylidene-p-toluenesulfonohydrazide, Nxe2x80x2-(1-phenylethylidene)-p-toluenesulfonohydrazide, Nxe2x80x2-(2-hydroxybenzylidene)-p-toluenesulfonohydrazide, Nxe2x80x2-diphenylmethylene-p-toluenesulfonohydrazide or Nxe2x80x2-(2-furylmethylene)-p-toluenesulfonohydrazide.
(10) The rubber composition as described in any of the above items (1) to (9), prepared by further compounding 0.1 to 5.0 parts by weight of at least one selected from antioxidants of naphthylamine base, p-phenylenediamine base, hydroquinone derivative, bisphenol base, trisphenol base, polyphenol base, diphenylamine base, quinoline base, monophenol base, thiobisphenol base and hindered phenol base.
(11) A pneumatic tire characterized by using a rubber composition prepared by compounding 0.05 to 5 parts by weight of at least one selected from the group consisting of the hydrazide compounds represented by Formulas (I) to (IV) described above per 100 parts by weight of a rubber component comprising natural rubber and diene based rubber as principal components.
(12) The pneumatic tire as described in the above item (11), wherein the rubber composition prepared by compounding 0.05 to 5 parts by weight of at least one selected from the group consisting of the hydrazide compounds represented by Formulas (I) to (IV) described above per 100 parts by weight of the rubber component comprising natural rubber and diene based rubber as principal components is used for a tire tread part.
(13) The pneumatic tire as described in the above item (12), wherein the rubber composition prepared by compounding 0.05 to 5 parts by weight of at least one selected from the group consisting of the hydrazide compounds represented by Formula (II) described above per 100 parts by weight of the rubber component comprising natural rubber and diene based rubber as principal components is used for a tire tread part.
(14) The pneumatic tire as described in the above item (13), wherein the hydrazide compound represented by Formula (II) described above is Nxe2x80x2-(1-methylethylidene)salicylohydrazide, Nxe2x80x2-(1-methylpropylidene)salicylohydrazide, Nxe2x80x2-(1,3-dimethylbutylidene)salicylohydrazide, Nxe2x80x2-(2-furylmethylene)salicylohydrazide, 1-hydroxy-Nxe2x80x2-(1-methylethylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(1-methylpropylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(1,3-dimethylbutylidene)-2-naphthohydrazide, 1-hydroxy-Nxe2x80x2-(2-furylmethylene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1-methylethylidene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1-methylpropylidene)-2-naphthohydrazide, 3-hydroxy-Nxe2x80x2-(1,3-dimethylbutylidene)-2-naphthohydrazide or 3-hydroxy-Nxe2x80x2-(2-furylmethylene)-2-naphthohydrazide.
(15) The pneumatic tire as described in the above item (12), wherein 30 to 70 parts by weight of carbon black having a specific surface area by nitrogen adsorption (N2SA) of 30 to 180 m2/g and a dibutyl phthalate absorption (DBP) of 60 to 200 ml/100 g is compounded per 100 parts by weight of the rubber component comprising natural rubber and diene based rubber as principal components; and the hydrazide compound is one in which A in Formula (I) described above is an aromatic group.
(16) The pneumatic tire as described in the above item (13), wherein 30 to 70 parts by weight of carbon black having a specific surface area by nitrogen adsorption (N2SA) of 30 to 180 m2/g and a dibutyl phthalate absorption (DBP) of 60 to 200 ml/100 g is compounded per 100 parts by weight of the rubber component comprising natural rubber and diene based rubber as principal components; and Y in Formula (II) described above is an aromatic group substituted with a hydroxyl group or an amino group.
(17) A hydrazone derivative represented by Formula (V):
ZC(xe2x95x90O)NHNxe2x95x90C(CH3)(CH2CH(CH3)2)xe2x80x83xe2x80x83(V)
wherein Z represents 3-hydroxy-2-naphthyl, 1-hydroxy-2-naphthyl, 2-hydroxyphenyl or 2,6-dihydroxyphenyl group.